I know this has been discussed before. I recorded over several nights at 192 kHz in supplied case attached to tree branch - particularly interested in bats. On nearly all recording have a rapid on/off pulsing noise at 53 kHz. On previous discussion it was concluded this was to do with writing to SD card (SanDisk ultra). Then I repeated with same card in a different location on a tripod in an open position without the case - same batteries, no further charging. This time I get a completely clean recording - not a hint of any noise. I have obtained new cards anyway, but puzzled as to why I had noise on the first occasion and not the second.
Automatic algorithms mistake the noise for soprano pupistrelle (albeit low probability)